As a process for producing the above-mentioned pyrrolidine derivative of general formula (2) or a salt thereof using compounds of the general formula (1): ##STR3## (wherein R is as defined above) as a starting material, a process is known (Japanese Kokai Publication Sho-61-100563) which comprises once synthesizing methyl 3-(1-cyano-1,1-diphenylmethyl)-1-pyrrolidinecarboxylate starting with 1-benzyl-3-(1-cyano-1,1-diphenylmethyl)-pyrrolidine and then converting the former to 3-(1-cyano-1,1-diphenylmethyl)-pyrrolidine. However, this process involves long steps and complicated operation and gives low yields, hence can hardly be said to be an industrial production process.
Another process is also known (Japanese Kokoku Publication Hei-07-72171) for producing 3-(1-carbamoyl-1,1-diphenylmethyl)-pyrrolidine by subjecting 1-benzyl-3-(1-carbamoyl-1,1-diphenylmethyl)-pyrrolidine to hydrogenolysis using palladium-carbon. However, it uses a large amount of palladium, which is expensive, and requires a long reaction time. Thus, it has problems as an industrial production process from the viewpoints of economy and productivity.
Furthermore, no process is known for producing 3-methanesulfonyloxypyrrolidine or a salt thereof by debenzylating 1-benzyl-3-methanesulfonyloxypyrrolidine, for producing 3-p-toluenesulfonyloxypyrrolidine or a salt thereof by debenzylating 1-benzyl-3-p-toluenesulfonyloxypyrrolidine, or for producing 3-n-butyryloxypyrrolidine or a salt thereof by debenzylating 1-benzyl-3-n-butyryloxypyrrolidine.
Accordingly, the development of a process for producing the above-mentioned pyrrolidine derivative of general formula (2) or a salt thereof in a simple and economical manner and with good productivity and high yields by debenzylating the above-mentioned compound of general formula (1) has been desired.